Re: [fluka-discuss]: Understanding origin of neutrons, photons, e+e-

From: <me_at_marychin.org>
Date: Mon, 3 Mar 2014 21:23:51 -0800 (PST)

Dear Alfredo,

I suppose your detector has a finite sensitive volume with respect to the mean
free path of the particles of interest.
n->gamma->e+/e- do not all happen on the same spot. The neutron travels a
distance before being captured; the gamma travels a distance before interacting.
With a big enough scoring volume, we count them all. With a small-enough scoring
volume, neutron won't get counted after it got captured.

To find out which photon and which electron come from the same ancestor neutron,
we do latching. Latching is done via stupre.f and/or stuprf.f.

:) mary

> On 03 March 2014 at 18:35 Alfredo Martin Castaneda Hernandez
> <amch031182_at_gmail.com> wrote:
>
> Dear FLUKA experts
>
> I have a fundamental question about the simulation,
>
> Let say I calculate the flux of particles in a certain volume of my detector
> using USRBIN option,
> for sure I can get fluxes for neutrons, photons, e+e-, muon, etc...
>
> For our purposes we are interested to count the contribution of radiation
> background in our detector,
> we assume most of that contribution will come from long living neutrons which
> can interact in the material and produce photons and those photons will
> produce electrons, and those electrons are
> the ones can cause a real signal in our detector, so the reactions will be
>
> n->gamma->e+/e-
>
> in our background contribution we are adding the contribution of those three
> particles, let
> say we have
>
> neutrons photons e+e- Total [Hz/cm2]
> 100 80 2 182
>
> (In reality we will add a sensitivity to each particle to account for the
> probability of generating
> a signal in our detector)
>
>
> The question is how we know if those photons or electrons were not produced
> by the same
> neutrons that we are considering, in such case a double counting will happen
> and we could ended up overestimating our background.
>
> So what we are assuming is that whatever enters the volume defined in USRBIN
> is what FLUKA
> counts, independently of what kind of reaction originated that particle
> outside the region of interest, but what would happen it a neutron goes
> inside the volume it interacts and produce a
> photons and then an electron, that contribution should in principle goes as
> one count in our flux right?
>
> Any help to understand this is highly appreciated.
>
> Thanks.
>
>
> --
> Alfredo
>
Received on Tue Mar 04 2014 - 07:24:25 CET